The present invention relates to industrial process control equipment. More specifically, the present invention relates to measurement transmitters which are used to measure various parameters (process variables) in industrial processes.
Measurement transmitters are used in processing and manufacturing plants to measure, for example, pressure, temperature, flow, density, viscosity and many other chemical, physical and electrical properties of fluids. Transmitters typically mount on tanks, pipes and other fluid vessels, and transmit a signal representative of a fluid property to a remote location such as a control room.
Transmitters usually include a sensor housing for sensor circuitry, and a transmitter housing for transmitter circuitry. The two housings are joined together at a flameproof mechanical joint. Generally the seals, software and electrical interfaces between the sensor circuitry and transmitter circuitry are not standardized, making it impractical to combine sensor and transmitter parts from different product lines.
Typically the inside of the sensor housing is open to the inside of the transmitter housing to allow wires to pass through the threaded joint. It is not practical in a plant environment to run field wiring directly to the sensor housing without use of a transmitter housing because the sensor housing, by itself, is not sealed and flameproofed from the environment. Further, the sensor circuitry is not able to transmit over a long distance.
Within a product line of pressure transmitters, the end user will typically be able to combine parts to make different combinations of pressure range, wetted materials and electrical or display arrangement. Additionally, this joining must normally be performed by the manufacturer. It is not, however, generally practical for the user to join sensor and transmitter parts from different product lines because there are electrical, software and mechanical incompatibilities.
There is a need for a transmitter arrangement where the sensor portion can be wired directly to a control system, or to other nearby components using a local area bus to increase functionality and scalability. There is also a need for transmitter components that can also be joined with component parts from other product lines without the need for significant modifications by the end user.
A unitized sensor module is provided which, in various aspects, can be wire directly to a control system or to other nearby components. An optional scalable transmitter module can couple to the sensor module to provide increased functionality and scalability for different applications. The sensor module includes a sensor output that can be configured to connect locally to the scalable transmitter module to form a transmitter, or to be wired directly to a remote receiver. A housing for the unitized sensor module carries circuitry in a cavity and a sensor that can sense a process variable. A feedthrough seals a fitting of the housing that provides an external connection to the sensor module.